1. Field of the Invention
The present invention relates to a ball joint apparatus used at junctions between mechanical elements of various machines and a manufacturing method therefor, and more particularly, to an improvement of means for fixing a socket to a housing in a ball joint apparatus having the housing and the socket.
2. Description of the Related Art
Various measures have conventionally been proposed to facilitate low-cost manufacture of ball joint apparatuses. In a connecting rod of a stabilizer for motor vehicle suspension described in Jpn. UM Appln. KOKAI Publication No. 61-176011 (Prior Art 1), for example, a circular projection for use as a housing is formed at an end portion of a metal-sheet rod body by burring or flanging. A socket is fitted into this projection. The socket has a concave spherical surface, which receives a spherical head of a stud ball. According to this prior art, the rod body and the housing can be integrally formed from one metal sheet.
In order to prevent the socket from easily slipping out of the housing, the socket, which should have an outside diameter larger than the inside diameter of the housing, must be press-fitted into the housing under a great load in the axial direction thereof. If the socket is press-fitted into the housing with too great a force, however, the spherical head of the stud ball, mated with the concave spherical surface of the socket, cannot rotate smoothly. It has been difficult, therefore, to press-fit into and fix the socket to the housing in a manner such that smooth operation of the stud ball is compatible with the practical strength of the socket in order to resist disengagement.
To secure the socket in place, an adhesive may be used. It is difficult, however, to secure the socket firmly with any adhesive available, since the material of the socket, i.e., engineering plastic which has mechanical properties suitable for sockets, is resistant to most chemicals and is hardly soluble in solvents. If the housing is made of iron to reduce the cost of the housing, its inner surfaces must be painted, and the paint film on the inner surfaces may decrease the adhesion of the socket to the housing.
In a pillow ball seat described in Jpn. UM Appln. KOKAI Publication No. 2-120209 (Prior Art 2), moreover, a ball seat member (socket) is inserted into a cylindrical piece for use as a housing. According to this prior art, a cap is bonded to that end face of the ball seat member which projects outside the cylindrical piece after the ball seat member is inserted into the cylindrical piece. The cap serves to prevent the ball seat member from slipping out of the cylindrical piece. In this prior art arrangement, however, the cap adds to the number of components of the ball joint apparatus, thus entailing an increase in cost. Further, the cap cannot prevent the ball seat member and the cylindrical piece from rotating relatively to each other.
The socket may possibly be fixed to the cylindrical housing by any other means than the arrangements of Prior Arts 1 and 2. Even in this case, however, the socket sometimes may move in the axial direction of the housing or rotate relatively to the housing, urged by loads in various directions which act on the housing and the stud ball during actual use of the ball joint apparatus. In some cases, this results in deformation or wear of the socket, so that the ball joint apparatus fails to maintain its desired characteristics.
In order to prevent the relative rotation of the housing and the socket, moreover, an arrangement may be proposed such that the inner peripheral portion of the housing and the outer peripheral portion of the socket are formed having a noncircular profile, whereby the socket can be fitted in the housing. In this case, however, a steel sheet or pipe for use as the material of the housing must be worked into a noncircular profile, so that manufacture requires a great deal of labor and also entails higher cost.